There often exists a need to deposit a substantially thick layer of copper upon copper as where a previously copper cast article is to be rebuilt or repaired. For example, in the casting of large industrial anodes molten copper is fed into a precasted, relatively cool mold which itself is made of copper. As copper anodes are made from the molds they become repetitively subjected to severe stresses caused by thermal cycling. In addition, some diffusion of metal occurs between the copper molds and the copper anodes being casted. As a result, some portions of the molds become rapidly degraded or depleted. In fact, it is not uncommon for the copper molds to have to be discarded after some ten days usage due to structural degradation or reshaping of the molds.
In some cases it is preferable to repair rather than to discard damaged molds due to considerations of availability, purchase lead time, and remoteness of location. Unfortunately, it has not heretofore been known how to effect repair since it has not been known how to deposit a relatively thick layer of copper upon a copper base so as to produce a structurally sound, unitary body.
There have heretofore existed methods of applying a thin layer of copper upon a copper substrate. For example, U.S. Pat. No. 3,742,585 teaches one such method wherein copper metal powder is sprayed in an inert atmosphere with a plasma gun onto a substrate of copper foil while the foil is in intimate contact with a cooling element. Methods have also been devised for depositing thin layers of copper on non-copper bases. U.S. Pat. No. 3,947,607, for example, teaches a method of forming copper on an aluminum alloy piston by spraying copper from an electric arc spray gun that produces molten particles of a size, velocity and heat content sufficient to produce an effective metallurgical reaction with the piston alloy so that the copper material becomes bonded thereto.
Although a layer of copper may be deposited on a non-copper metallic base with a spray gun, such method is not effective in depositing a thick layer of copper such as one greater than film sizes on a copper base. Where molten copper is sprayed onto a surface area of a copper base larger than the spray impact area itself to an appreciable thickness, it is soon discovered that the deposited material lacks structural integrity and can easily become broken off from the base material. Upon examination it can be determined that this is due to the presence of appreciable quantities of copper oxides within the layer of deposition. The formation of these oxides could, of course, be avoided by carrying out the deposition process in an inert atmosphere as done in the film deposition process described in the first mentioned patent. Environmentally controlled chambers, however, are often unavailable in the field just as casting facilities are not available as previously mentioned. The present invention thus is directed at alleviating these problems by providing a method of effectively depositing copper on copper bases which may be conducted without casting facilities or environmentally controlled chambers.